High pressure valves such as high pressure fuel injectors for use in direct injection of fuel into internal combustion engines, have requirements for very high solenoid forces due to the fact that such valves must operate very fast. Since the valves open into high pressure volumes, they need high spring forces acting in a direction typically opposite to opening to bias the valves closed and to seal the valve. In order to work against these opposing forces, dual working gap solenoid stators and armature combinations have been used. The dual gap principle allows both gaps to provide useful force to attract the armature to the stator.
In prior art high pressure valves, the armature has been a simple flat disk design. The reasons are many, from ease of fabrication to ease of design. Such a flat disk, however, is not particularly economical about its use of magnetic material and this makes the armature excessively heavy. In addition, when the armature seats against the pole pieces, any fluid captured therebetween must be squeezed out slowing the movement of the armature. Spaced apart apertures through the disk to remove such fluid unfortunately provide a high resistance path for the fluid to take as it flows from one side of the armature to the other.
Magnetically the flat disk is subject to the circulation of eddy currents and since it has excessive magnetic material, energy dissipation in the magnetic path is costly. Structurally, the flat disk is relatively flimsy in the bending direction. With the dual gap and more particularly since the second gap is at the outer edge of the disk armature, the magnetic force in this gap has the maximum possible moment arm for bending in the cross sectional direction of the armature. When this happens, unsymmetrical magnetic gaps are created and performance of the magnetic circuit is degraded. Still other disadvantages arise since the length of the magnetic gap is also the stroke of the armature/needle in the opening and closing of the valve, the uneven magnetic gaps can have severe mechanical effects by limiting the travel of the armature and applying uneven stop forces to the armature.
In order to overcome these and other disadvantages the spoked armature of the present invention is used in an electromechanical fuel injector having a solenoid actuating system for opening and closing the valve. The solenoid frame member is cylindrical and even though it is an integral structure it has co-axially aligned inner and outer tubular members radially displaced from each other and joined together at a one end forming a closed end. A coil means is located in the volume created between the tubular members and extends substantially the full depth of the frame from the open end to the closed end. This combination of a coil means and solenoid frame member forms a stator member wherein each of the tubular members form outer and inner concentric pole piece members respectively at the open end. The coil means is sealed in the frame to reduce the deterioration of the coil by the fluid in the injector.
Axially aligned with the stator and displaced therefrom is a valve seat means. An elongated needle having a valve member at one end extends axially from the valve seat means toward the stator member. Located in the inner tubular member of the solenoid frame member is a spring to bias the elongated needle means against the valve seat. A spoked armature means is secured to the elongated needle at its end opposite the valve member. The spoked armature has a central hub and a concentric ring connected to the hub by means of a plurality of spokes. The hub is magnetically coupled to the inner concentric pole piece and the ring is magnetically coupled to the outer concentric pole piece providing dual working gaps. The spoked armature is attracted to the pole pieces when the coil means is actuated by an electrical signal to axially displace the valve member from the valve seat means thereby opening the valve.
In another embodiment, a magnetic disk is interposed the stator and the armature. The disk has a central aperture and substantially enclosing the coil means at the open end of the stator member. The disk is magnetically connected to the outer concentric pole piece member providing a magnetic path to magnetically locate the outer concentric pole piece adjacent to the inner diameter of the central aperture of the disk which is chamfered to provide a concentrated circular pole thus concentrating the working gaps.
These and other advantages of the spoked solenoid armature will become apparent in the following drawings and detailed description.